a. Field of the Invention
The instant invention generally relates to devices and methods for treating electrophysiological diseases of the heart. In particular, the instant invention relates to devices and methods for controlling and monitoring epicardial ablation for the treatment of atrial fibrillation.
b. Background Art
It is well known that atrial fibrillation results from disorganized electrical activity in the heart muscle (the myocardium). The surgical maze procedure has been developed for treating atrial fibrillation, and involves the creation of a series of surgical incisions through the atrial myocardium in a preselected pattern so as to create conductive corridors of viable tissue bounded by scar tissue.
As an alternative to the surgical incisions of the maze procedure, transmural ablations of the heart may be used. Such ablations may be performed either from within the chambers of the heart (endocardial ablation), using endovascular devices (e.g., catheters) introduced through arteries or veins, or from outside the heart (epicardial ablation) using devices introduced into the patient's chest. Various ablation techniques may be used, including, but not limited to, cryogenic ablation, radio frequency (RF) ablation, laser ablation, ultrasonic ablation, and microwave ablation. The ablation devices are used to create elongated transmural lesions—that is, lesions extending through a sufficient thickness of the myocardium to block electrical conduction—forming the boundaries of the conductive corridors in the atrial myocardium. Perhaps most advantageous about the use of transmural ablation rather than surgical incision is the ability to perform ablation procedures without first establishing cardiopulmonary bypass (CPB).
In performing the maze procedure and its variants, whether using ablation or surgical incisions, it is generally considered most efficacious to include a transmural incision or lesion isolating the pulmonary veins from the surrounding myocardium. The pulmonary veins connect the lungs to the left atrium of the heart, joining the left atrial wall on the posterior side of the heart.
This location creates significant difficulties for endocardial ablation devices for several reasons. First, while many of the other lesions created in the maze procedure can be created from within the right atrium, the pulmonary venous lesions must be created in the left atrium, requiring either a separate arterial access point or a transeptal puncture from the right atrium. Second, the elongated and flexible endovascular ablation devices are difficult to manipulate into the complex geometries required for forming the pulmonary venous lesions and to maintain in such positions against the wall of the beating heart. This is very time-consuming and can result in lesions that do not completely encircle the pulmonary veins or that contain gaps and discontinuities. Third, because elongated ablation devices are often pre-shaped to maintain a minimum curvature, a surgeon must create an incision in the patient's body sufficiently large to accommodate not only the width of the ablation device, but also its curvature. Finally, the heat generated by endocardial devices that flows outward through the myocardium cannot be precisely controlled and can damage extracardiac tissues such as the pericardium, the phrenic nerve and other structures.
What are needed, therefore, are devices and methods for forming lesions that isolate the pulmonary veins from the surrounding myocardium that overcome these problems. The devices and methods will preferably be utilized epicardially to avoid the need for access into the left chambers of the heart and to minimize the risk of producing thrombus.
Additional aspects of the present invention are directed to devices and methods for ablating tissue. Ablation of heart tissue and, specifically, ablation of tissue for treatment of atrial fibrillation is developed as a particular use of these other aspects of the present invention.